1. Field of the Invention
The present invention relates to a heat treatment apparatus and a cleaning method of the same, and more particularly to a heat treatment apparatus in which reactive products are prevented from attaching thereinto and a cleaning method of the same.
2. Description of the Related Art
A silicon oxide film (SiO2 film) or a silicon nitride film (Si3N4 film) is used in various sections of a semiconductor device.
An SiO2 film is produced by resolving alkoxysilane in a decompression CVD device, etc. An unreacted substance of alkoxysilane [(SiCxHyOz)nx=0.1 to 2, y=1 to 15, z=0.1 to 5, n greater than 0] attaches into the CVD device in a process for producing an SiO2 film. Such a substance comes off in a process for forming a film, and becomes particles. This process has the drawback of lowering the quality of to-be-manufactured semiconductor devices and of having a low overall yield.
An Si3N4 film is produced by a reaction of, for example, ammonia (NH3) and dichlorosilane (SiH2Cl2) in the CVD device. While a silicon nitride film is being formed, ammonia chloride (NH4Cl) may be in a state of solidity in a low-temperature section of a reaction tube. If the ammonia chloride is sublimated when loading a semiconductor substrate and attaches to the semiconductor substrate, it becomes a source for particles to be formed on the surface of the substrate in a process for forming a film. Particles which have been formed as a result of a reaction of the sublimated ammonia chloride and moisture within the atmosphere attach onto the semiconductor substrate, resulting in a defective feature of the semiconductor device.
The temperature and the exhaust conductance of a manifold of a reaction tube, the periphery of an exhaust section and an exhaust pipe are lower than those of a film-forming area where a wafer boat is arranged. Therefore, a lot of reactive products are likely to attach into those sections.
Accordingly, the conventional heat treatment apparatus has been taken apart in order to clean its composing elements for large scale maintenance, while the operations of the apparatus are suspended for a long period of time. Therefore, only a low operational rate of the apparatus has been achieved.
In order to prevent the apparatus from being operated at a low operational rate while cleaning its composing elements, Unexamined Japanese Patent Application KOKAI Publication No. H5-214339 discloses a method of cleaning an apparatus forming silicon nitride films with using HF gas. In addition to this, Unexamined Japanese Patent Application KOKAI Publication No. H4-333570 discloses a method of cleaning an apparatus by removing nitrogen silicon therefrom with using HF gas. The references cited disclose merely a method of cleaning an apparatus by removing (SiCxHyOz)n with using HF gas and by removing nitrogen silicon. In the references, no disclosure has been made to a method of forming films in a heat treatment apparatus and a method of cleaning the same. The references do not even disclose a technique for preventing HF gas used for the cleaning from contaminating the environment.
In various processes for manufacturing semiconductor devices, a two-layered film, such as SiO2/Si3N4, etc. or three-layered film, such as SiO2/Si3N4/SiO2, etc. is used. Conventionally, an SiO2 film and an Si3N4 film have been produced in different apparatuses. Thus when transferring a wafer from one apparatus to the other, a natural oxide film and particles obviously attach onto the surface of the wafer. Thus causes the problem of lowering the quality of to-be manufactured semiconductor devices and of having a low overall yield
Accordingly, it is preferred that an apparatus can from the SiO2 film together with the Si3N4 film. However, no proposal has yet been made for an apparatus in which particles are prevented from attaching thereinto.
Accordingly, the present invention has been made in consideration of the above, in order to clean a heat treatment apparatus with efficiency.
An object of the present invention is to provide a method of efficiently cleaning an apparatus capable of producing various kinds of films.
Another object thereof is to provide a technique for cleaning a heat treatment apparatus with using HF gas while preventing the used HF gas from contaminating the environment.
In order to achieve the above objects, according to the first aspect of this invention, there is provided a heat treatment apparatus, comprising
a reaction tube which can contain an object to be heat-treated;
an exhaust pipe, one end of which is connected to the reaction tube, for exhausting gas contained in the reaction tube;
a reactant-gas supplying pipe, which is conducted into the reaction tube, for supplying reactant gas into the reaction tube;
an HF-gas supplying section which includes
an HF pipe connected to a gas source for hydrogen fluoride,
an HF valve which controls to supply hydrogen fluoride from the gas source and which is arranged in the HF pipe, and
an inlet which conducts, into the exhaust pipe and/or the reaction tube, the hydrogen fluoride supplied from the gas source through the HF pipe,
wherein the HF valve is open and the hydrogen fluoride gas is conducted from the gas source into the exhaust pipe and/or the reaction tube, thereby cleaning inside of the exhaust pipe and/or the reaction tube.
In the structure, an inlet for supplying HF gas is arranged in the reaction tube separately from the reactant-gas supplying pipe. When an HF valve is open, HF gas can be conducted into the reaction tube and/or the exhaust pipe which can then be cleaned. Therefore, the heat treatment apparatus can be cleaned with simple treatments only.
In the structure disclosed in Unexamined Japanese Patent Application KOKAI Publication No. H5-214339, as shown in FIG. 2 included in the Publication, HF gas and reactant gas are conducted into a reaction tube from an identical gas-supplying section. Therefore, the reactant gas is fearfully contaminated in a process for forming a film.
Unexamined Japanese Patent Application KOKAI Publication No. H4-333570 suggests (1) a method for conducting HF gas into an apparatus which can form thin films and (2) a method for conducting HF gas into a cleaning apparatus by inserting the apparatus itself into the cleaning apparatus. However, no disclosure has been made to a xe2x80x9cstructure for efficiently conducting HF gas into the apparatus so as to clean the apparatusxe2x80x9d.
The other end of the exhaust pipe may be split into a first and second vents; and
a valve may be arranged between the first and second vents, may conduct exhaust gas into the second vent when HF gas is exhausted, and conduct exhaust gas into the first vent when no HF gas is exhausted.
According to this structure, the products produced while forming a film and the HF gas used for cleaning the apparatus can separately be heat-treated. An HF gas scrubber may be used as the second vent, whereas a scrubber for any other kind of gas may be used as the first vent.
In the heat treatment apparatus, there may be arranged a plurality of traps which are arranged on the exhaust pipe and which remove a reactive product within the exhaust pipe, and
a pressure control valve which is arranged between the plurality of traps and which maintain pressure within the reaction tube and the exhaust pipe at a fixed value.
It is necessary to maintain the pressure within the reaction tube and the exhaust pipe at an appropriate value in order to form a film and clean any part of the apparatus. The pressure control valve controls the pressure by itself or together with any other device. Since the pressure control valve is arranged between the plurality of traps, the reactive products are prevented from attaching to the pressure control valve (normally, the reactive products easily attach thereto).
The reaction tube includes an inner tube, whose upper end is open, and an outer tube, which surrounds the inner tube with a predetermined space and whose upper ends is closed. In this case, it is preferred that the inlet conducts HF gas into the inner tube, and the exhaust pipe is connected to the outer tube and exhausts gas from the gap between the inner and outer tubes. In having such a structure, the HF gas from the inlet cleans inside of the inner tube toward the upper end of the inner tube, and reaches the exhaust pipe through the space between the inner tube and the outer tube. Thus, cleaning what is so-called xe2x80x9cvertical double tubesxe2x80x9d can be performed with efficiency.
It is preferred that the inlet is arranged in a position adjacent to an intake (the most upstream side) of the exhaust pipe. Conductance varies in the portion through which exhaust gas passes from the reaction tube to the exhaust pipe. This results in reactive products easily attaching into the periphery of the intake of the exhaust pipe. When the inlet is thus arranged in a position adjacent to the intake of the exhaust pipe, the products which have attached into a bent part can be removed with efficiency.
In a case where the exhaust pipe includes at least one bent part, it is preferred that the inlet is arranged on an upstream side of a gas-flowing path and adjacent to the bent part of the exhaust pipe. Conductance of the bent part is low, therefore, a reactive product is likely to attach to the part. If the inlet is arranged adjacent to the bent part on the upstream side of the gas-flowing path, the products which have attached to the bent part can be efficiently removed.
In a case where the trap is arranged on the exhaust pipe, the inlet is preferably arranged adjacent to the trap on the upstream side of the gas-flowing path. Conductance of the trap is also low, therefore, a reactive product easily attaches thereto. If the inlet is arranged adjacent to the trap on the upstream side, the products which have attached to the trap can be efficiently removed.
The reactant-gas supplying pipe conducts alkoxysilane into the reaction tube in order to form a silicon oxide film on the object, and/or conducts ammonia and a silicon compound (for example, monosilane (SiH4), dichlorosilane (SiH2Cl2), silicon tetrachloride (SiCl4)) into the reaction tube in order to form a silicon nitride film on the object, and
the reaction tube forms a silicon oxide film on the object by resolving alkoxysilane, and/or forms a silicon nitride film on the object by a reaction of ammonia and a silicon compound.
In such a structure, a silicon oxide film and a silicon nitride film can successively be formed in a single one heat treatment apparatus. Furthermore, the products produced in the process for forming the silicon oxide film and the products produced in the process for forming the silicon nitride film are efficiently removed with using HF gas.
The exhaust pipe may include an SiO2 product trap (for example, a disk trap), in the exhaust pipe, which removes a reactive product produced by resolving alkoxysilane within the exhaust pipe,
an SiN product trap (for example, a water trap) which removes a reactive product produced by a reaction of ammonia and a silicon compound within the exhaust pipe; and
a heater which heats up the SiO2 product trap in a range between 100 to 150xc2x0 C.
The pressure control valve is preferably arranged between the SiO2 product trap and the SiN product trap and is heated up by the heater.
The pressure control valve is preferred to maintain the pressure within the exhaust pipe at a pressure value of 10 kPa or higher.
The apparatus may further include a heater which heats up the exhaust pipe in a range from 100 to 200xc2x0 C.
The apparatus may further include a heater which heats up the reaction tube and which heats up the exhaust pipe in a range from 100 to 200xc2x0 C.
The apparatus may further include a pressure controller which controls pressure of hydrogen fluoride within the exhaust pipe to be fluctuated. The pressure of the hydrogen fluoride within the exhaust pipe is fluctuated, therefore, the hydrogen fluoride spreads over the exhaust pipe even in a part where the conductance is low or in a dead space (a part, such as a cavity, a space between connected portions, etc., through which gas does not flows), resulting in cleaning the entire apparatus evenly.
The pressure controller controls the pressure within the exhaust pipe to be fluctuated in a range, for example, 0.1 kPa to 30 kPa. Since the pressure is fluctuated in such a range, the hydrogen fluoride thus spreads over.
The pressure controller is preferred to control the pressure within the exhaust pipe to be fluctuated in such a way that a period at which the pressure is 10 kPa or higher and a period at which the pressure is lower than 10 kPa are cyclically repeated, and that the period at which the pressure is 10 kPa or higher can be obtained longer than the period at which the pressure is less than 10 kPa.
The heat treatment apparatus of this invention may further include a purge-gas supplying section which supplies purge gas into the exhaust pipe and/or the reaction tube; and
a controller which repeats, after the HF-gas supplying section stops supplying hydrogen fluoride, a plurality of cycles of exhausting and supplying purge gas into the exhaust pipe and/or the reaction tube by the purge-gas supplying section and the exhaust pipe, and which supplies film-forming gas by the film-forming gas supplying section during the plurality of cycles.
The HF gas is preferred to be purged immediately after cleaning is completely performed. In the above structure, the film-forming gas is supplied during the plurality of cycles of exhausting and supplying the purge gas into the exhaust pipe, thus, the exhaust pipe can be purged of the exhaust gas in a short time.
The film-forming gas supplying section supplies alkoxysilane as the film-forming gas, while the purge-gas supplying section supplies nitrogen gas as purge gas.
According to the second aspect of the present invention, there is provided a method of cleaning at least one of a reaction tube which is included in a heat treatment apparatus and an exhaust pipe which is connected to the reaction tube, the method comprising:
a loading step of loading an object to be heat-treated into the reaction tube;
a first film-forming step of forming a first film on the object, by supplying first reactant gas into the reaction tube;
a second film-forming step of forming a second film on the object, after stopping supplying the first reactant gas into the reaction tube and supplying second reactant gas which differs from the first reactant gas; and
a cleaning step of removing a product produced in the first film-forming step and a product produced in the second film-forming step which have attached to at least one of the reaction tube and the exhaust pipe, by exhausting gas contained in the reaction tube through the exhaust pipe and supplying hydrogen fluoride gas into at least one of the reaction tube and the exhaust pipe.
During the cleaning process, it is preferred that the method includes
a raising step of raising temperature of the reaction tube and heating up the exhaust pipe in a range from 100 to 200xc2x0 C.; and
a maintaining step of maintaining pressure within the exhaust pipe in a range between 10 kPa to 30 kPa.
The method may comprise a cleaning step of cleaning at least one of the reaction tube and the exhaust pipe by supplying hydrogen fluoride gas thereinto, while controlling the pressure within the exhaust pipe to be fluctuated in a range between 0.1 kPa and 30 kPa.
In this case, it is preferred that the method comprises a controlling step of controlling pressure within the exhaust pipe to be fluctuated in such a way that a period at which the pressure is 10 kPa or higher and a period at which the pressure is less than 10 kPa are cyclically repeated, and that the period at which the pressure is 10 kPa or higher can be obtained longer than the period at which the pressure is less than 10 kPa.
The film-forming step includes a step of forming, on an object to be heat-treated, a silicon oxide film by resolving alkoxysilane, and
the second film-forming step includes a step of forming, on the object, a silicon nitride film by a reaction of ammonia and a silicon compound.
In this case, the cleaning step includes a step of exhausting the reaction tube through the exhaust pipe and a step of supplying hydrogen fluoride into at least one of the reaction tube and the exhaust pipe, thereby removing a reactive product which is produced by resolving alkoxysilane and a reactive product which is produced by a reaction of ammonia and a silicon compound and both of which have attached to at least one of the reaction tube and the exhaust pipe.
Impurities being exhausted are removed in various positions of the exhaust pipe by a trap, and pressure of hydrogen fluoride gas is controlled in a position between the plurality of traps, by controlling an opening degree of a gas-flowing path of the exhaust pipe.
The exhaust pipe is decompressed, after supplying the hydrogen fluoride gas,
film-forming gas is supplied into at least one of the reaction tube and the exhaust pipe, after repeating supplying purge gas and decompressing the exhaust pipe for a given number of times, and
supplying purge gas and decompressing the exhaust pipe are repeated for a given number of times again, thereby removing the hydrogen fluoride gas.
In this case, the purge gas is composed of nitrogen gas, etc., while the film-forming gas includes alkoxysilane, etc.